Easiest way is to use the zedge program. You browse ringtones, etc. and then when you select one to download, it asks if you want to set it as your global ringtone or just for a specific contact.

Yes, that is a fairly simple way to do it. RingDroid is another app that can make ringtones.

I make my own ringtones and notifications on my PC using Audacity. Ringtones can be made from any audio file then converted to an mp3 file. Ringtones are best when about 22 seconds long; notifications are best when 5 seconds long.